Feathering propeller



April 1942- 1:. MARTIN ETAL 2,280,713

FEATHERING PROPELLER 4 Sheets-Sheet l Filed June 12, 1937 .llllllllllm new w W; w mflmd N R WEE m mm M m if

April 21, 1942. E. MARTIN E AL 2,280,713

FEATHERING PROPELLER Filed Jun 12; 1937 4Sheets-Sheet 2 INVENTORS MUPPHYQBEBbE r19 Mar): BWZE/mar/Lyderaon vm'im April 21, 1942. E. MARTIN ET AL 2,280,713

FEATHERING PROPELLER Filed June 12, 1937 4 Sheets-Sheet 3 INVENTORS Mmr'ayll'fie be m 9% i. M

A TTORNEY April 21, 1942. E. MARTIN ETAL 2,280,713

. FEATHERING PROPELLER Filed June 12, 1937 4 Sheets-Sheet 4 r eM'arLzlrz (fob? Ems/winders;

ATTORNEY Patented Apr. 21, 1942 rsa'rnsame raorsua'n Eric Martin, West amel-a, John Elmer Anderson, Portland, and Glastonbury, Conn,

28 Claims.

This invention relates to improvements in controllable pitch aeronautical propellers and has particular reference to a hydraulically operated controllable pitch propeller which may be feathered.

An object of the invention resides in the provision of a propeller of the character specified which has a normal operating range and a feathering range beyond the normal-operating range.

A further object resides in the provision of a propeller of the character specified which may be controlled in its operating range and put into and brought out of its feathered condition by changing the pressure of the hydraulic fluid supplied to the controlling mechanism of the propeller.

Murray 0. Beebe, South assignors to United Air.- oraft Corporation, East Hartford, Conn., a cor- Duration of Delaware Application June 12, 1937, Serial No. 147,972

A still further object resides in the provision of a propeller of the character specified which may be positively put into and brought out of its feathered condition by the application of hydraulic fluid under pressure to the propeller operating mechanism.

An additional object resides in the provision of a propeller of the character specified which may be controlled in its normal operating range, I

range of pitch adjustment, and hydraulic fluid under pressure is being admitted to increase the pitch.

Fig. 3 is a somewhat schematic and expanded illustration onan enlarged scale of the propeller included mechanism for controlling the application of the hydraulic fluid andv illustrates the positions of the parts when the propeller is in'its normal operative range of pitch adjustment as shown in Fig. 2, and hydraulic fluid is being drained to allow centrifugal force to reduce the pitch. a

Fig. 4 is a view similar to Fig. 3 and shows the positions of the parts when the propeller is at the upper limit of its operative range of pitch ad- .iustment or is in transition between its ordinary operating range and the bl of pitch adjustment.

Fig. 5 is a view similar to Figs. 3 and 4 and shows the positions of the parts when the prode feathering range peller is being brought out of its feathered condition and, I

Fig. 6 is a cross-sectional view taken onthe line H of'Fig. 2.

feathered, and brought out of feather by the application of hydraulic fluid at different pressures through a single hydraulic fluid supply line leading to the propeller' operating mechanism.

Other objects and advantages will be more particularly pointed out hereinafter or will become apparent as the description proceeds.

In the accompanying drawings, in which like reference numerals are used to designate similar parts throughout, there is illustrated a suitable mechanical embodiment of what is now considered to be the preferred form of the invention. The drawings, however. are for the purpose of illustration only and are not to be taken as limiting the invention the scope of which is to be measuredentirely by the scope of the appended claims.

In the accompanying drawings Fig. 1 is an elevational view of a fragmentary portion of an engine and aeronautical propeller and a schematic illustration of means for supplying and controlling the supply of hydraulic fluid to the propeller.

Fig. 2 is an elevational view of an improved controllable pitch feathering type propeller con- Referring to the drawings in detail and particularly to Fig. 1 the numeral I 0 generally indicates a suitable propeller driving engine pro-' vided with a hollow power shaft or crank shaft l2 rotatably supported in the engine casing by suitable means such as the anti-friction ballbearing i4 and projecting from the engine to v support and drive an aeronautical propeller generally indicated at It.

In the case of a geared engine, as illustrated in Fig. 2, a propeller shaft i1 is telescopically associated with the end of the crank shaft and is driven thereby.

structed according to the idea of this invention,

certain portions being broken away and shown in section to better illustrate the construction thereof, and showing the positions of the parts when the propeller is in its normal operative The propeller it, which constitutes the main portion of the subject matter of this invention, and which will subsequently be described in greater detail, is a controllable pitch propeller adapted to be used with a speed responsive device to provide a constant speed engine propeller combination, and is actuated in at least one direction by a suitable hydraulic mechanism to which hydraulic fluid is supplied from any suitable source of hydraulic fluid under pressure. In most installations pressure is applied to the hydraulic fluid by a suitable mechanism driven by the engine, and a suitable sump or reservoir is provided for receiving hydraulic fluid drained from the propeller operating mechanism.

a In the arrangement illustrated in Fig. 1 a speed responsive device, such as the centrifugal governor I8, is provided and is driven by the envenient fixed portion of ing pressure.

design, may be manually controlled by a suitable device, such as is generally indicated at 22, to vary the governed speed.

Fluid under pressure may be supplied from any suitable source and in the arrangement illustrated in the drawings is supplied by a suitable engine driven mechanism such as the pump it and is led from the pump through a suitable conduit to a governor operated valve, the construction of which is well-known to the art, and iromthe governor operated valve, through suit able conduits and channels, to the propeller controlling mechanism.

In the construction illustrated, the hydraulic fluid, which may be engine lubricating oil or any other suitable fluid, is led from the governor controlled valve through the conduit 28 to a suitable pressure responslvevalve, generally indicated at 28, and from the valve til through a conduit or channel 30 to the interior the hollow power shaft l2 through a suitable bearing connection or slip ring 32. The valve 28 may be incorporated in the governor base or in some conthe engine if desired. The shaft it contains two concentric tubes M and 36 of diilerent diameters and the space within the shaitsurrounding the outer tube lit or between the shafts l2 and il in a geared engine, is blockedupon the rear side of theconnectlon 32,

as indicated at 38, so that the hydraulic fluid forced into the shaft flows through the channel between the interior of the outer shaft and the drain tube 36 or inner shaft, to the propeller controlling mechanism. Hydraulic iiuld under the control oi the governor controlled valve may move to and from the propeller through this 1 channel as the valve connects the channel with the pump 24 or with the drain 89. The space between-the tubes 34 and 36 constitutes a drain line which continues past the plug it and empties into the sump, generally indicated at so. by means schematically shown as a conduit 31. The sump 40 itself, or a container connected therewith, constitutes a reservoir irom which the hydraulic fluid is drawn by the pump 2! to supply the propeller controlling mechanism.

.- The pump 24, which may, if desired, be assisted by one or more booster pumps located in favorable positions along the fluldline leading from the pump 24 to the shaft l2, for example in the governor base, supplies hydraulic fluid to the propeller controlling mechanism at a substantially constant pressure, the pressure used in some installations being in the neighborhood of ,200 pounds to the square inch. This pressure range will be hereinafter referred to as the works In carrying out the idea of this invention means have been provided for supplying hythan the working pressure, for purposes which will presently appear. Such means may take they auxiliary pump 42 has its inlet connected by means of a suitable conduit 88 with the sump or reservoir All, and its outlet connected by a similar conduit 46 with the valve 26 which is in turn connected-by the conduit to and the connection ,32 with the interior of the outer shaft l?! or W.

I The governor, which maybe of any well-brown the valve 28 is provided interiorly thereoi with a hollow cylindrical part ll, provided with ports 18 and 50, the ports 48 being located in the side of the part 51 onthe valve outlet side of the valve diaphragm iii, while the port he is located in the end oi the cylindrical part on the inlet side of the valve diaphragm 52. A plunger or piston member 54 is slidably mounted in the interior of the cylindrical part t! and is urged, by suitable means such as the coil spring 56, to a position in which it closes the port 58.

When the auxiliary pump 42 is inoperative, hydraulic fluid flows from the pump 24 through the governor controlled valve, the conduit it and entrance aperture 53, to the interior of the cylinto the connection 332. When the auxiliary pump i2 is operative to apply pressure to the hydraulic fluid greater than the working pressure, the piston member lid is forced to the left, as viewed in Fig. l, against the action of the spring bit, to a position in which the port is connected with the ports at! through the interior of the cylindrical member ll, and the entrance aperture 58 for hydraulic fluid at the working pressure is completely cut oil from the ports 5B and 48 and the high pressure fluid. The hydraulic fluid willthen how from the outlet of the pump 42 through the conduit it to the inlet chamber of the valve 28, through the ports 56 and 48 to the outlet chamber of the valve and thence through the conduit to the connection 32 and into the interior or the hollow power shaft. The spring 56 has a rate such nect the port 50 with the ports 48 until the pres- ,sure exerted by the pump t2 exceeds the working pressure by a preselected amount.

. The auxiliary pump d2 ls efiective to apply pressure to the hydraulic fluid in at least two ranges above the working pressure. In some installations the lower pressure applied by the auxiliary pump is in the neighborhood of 300 pounds to the square inch, which pressure range will be hereinafter referred to as the feathering high pressure. In the same installations the sec ond pressure range imposed by the auxiliary pump ll? may be in the neighborhood of 600 pounds to the square inch,which pressure range will hereinafter be referred to as the restoring high pressure.

The controllable pitch propeller I6 is illustrated in detail in Figs. 2 to 6 inclusive. In the construction illustrated a hub member 88 is mounted upon the projecting end of the hollow power shaft it or propeller shait H and suitably :liil

.draulic iiuld to the propeller at pressures other secured-thereon against both axial and rotational movements with respect to the power shaft. The hub member is provided with a plurality of hollow radially extending arms; as indicated at M, and upon each of these arms there is mounted a propeller blade, as indicated at 64, supported for rotating or oscillating movements about the axis of the respective arm. Asleeve, as indicated at (it, is disposed between the hollow base or root portion oi each of the propeller blades and the respective arm on the hub member, the sleeves being inserted in the propeller blades in such a manner that they are relatively immovable with respect thereto. Each oi. the sleeve members 66 has a flange portion, as indicamd at 68, eirtend-v ins between the inner end or the respective propeller blade 6d and a suitable bearing surface provided on the adjacent portion of the hub I ceivea the cylindrical members 84 and member 60. Aring member lll surrounds each of the flanges 6' and is resiliently connected therewith against relative rotation, and is provided at one side thereof with a gear sector as indicated at 12.

The propeller blades are retained upon the hub member Ill by a suitable barrel member 14, preferably formed in two portions and secured together by suitable means such as the clamp bolt H. The barrel member i4 is provided with inwardly turned portions which overlie the flanged base ends of the propeller blades, suitable antifriction means being interposed between the inwardly turned portions of the barrel member and the flanged ends 01' the propeller blades, in a manner well-known to the art, to provide for relatively free rotation of the propeller blades about the respective arms 5!. Suitable packing means, as indicated at Wand between the barrel member l4 and the hub member 80, and the barrel member and the base por tions of the propeller blades #4, to constitute the barrel member N a lent: proof receptacle for the reception of hydraulic fluid from the-propeller operating mechanism.-

The gear sectors .12 on the ring members it! have gear teeth inclined at an angle to the axis of rotation of the propeller, which mesh with similarly disposed gear teeth on a ring gear 82 integrally associated with a portion of the, barrel member to positively restrain the member 88 against rotation relative to the barrel member. 2 A plurality of rollers form cam followers, as indicated at "2, which extend, through each pair or cooperating cam slots 86 and Ill. Each cam follower I 02 indicated at received in walls of a double walled piston I", which 112-- is mounted upon a pin or axle, as I04, the opposite ends of which are pace between its inner and outer walls and co- :operates with the cover member or cylinder 84 hydraulic to constitute an expansible chamber mechanism for turning the propeller blades about the arms 82. V

Movement oi the piston I" in the cylinder ll, in an axial direction will move the cam followers through the cam slots 8' and 80 to impart r0 tational movement to the member 84 with respect to the member I8. As the member 04 is operatively connected with the propeller blades through the ring gear 82 and respective gear sectors l2, rotation 01' the member 84 incident to axial movements of the piston I06 rotates: the

propeller blades 84 about the axes of the respective arms I, which axes preferably coincide with respective blades.

the longitudinal axes of the Suitable antifriction means, such as th ball. bearings I" and III are preferably interposed between the members 04 and to,insure rela- 94, which is secured 88 in the tlvely i'ree rotation of the member I4 with respect tothe member 88.

While rotation of the propeller blades N about the arms I! has been referred to as an incident of the axial or longitudinal movement of the piston I, it does not necessarily follow that movement of the piston is always the result 01' of hydraulic fluid under pressure thereto, since the piston may at times be moved by other forces such as the centrifugal forces of the propeller blades themselves acting through the cam and the cam followers.

The means for directing the application of hyerally indicated at HI, and a by-pass valve. genan, is interposed suitable apertures provided in the of the power shaft serves the aizplanei The valve housing .treme end of erally indicated at Hi, all disposed in a valve housing generally indicated at Hill.

The action and cooperation of these various elements is such that when only the working pressure is applied to the hydraulic fluid, the propeller will function as a controllable pitch or constant speed propeller within a normal pitch range determined by the low pitch limit stop I22, which is secured indirectly to the barrel l4 and coacts with a lug on the movable cam 8|, and-the intermediate pitch limit stop Ill. When the feathering pressure is applied to the hydraulic fluid, the propeller blades will be immediately turned to a feathered position in which they'are disposed substantially parallel to the axis of the propeller shaft and hence provide a minimum drag resistance, and when the restoring pressure is applied to thehydraulic fluid. the blades are returned to their operative position and the propeller may again function as a constant speed propeller or may, if. desired, be placed under the operator of the. vehicle. The fea ture of feathering the propellerblades has. many advantages well-known to the art provided without excessive drag i'orces due to windmilling propellers.

I20 comprises an inner tubular member I24 and an outer concentric cylindrical member 1,28 slidably received in the piston 186, connected at one end to a flared bell-like member I 28,,the tubular casings for the valves H2, H8 and the intermediate pitch limit stop I ll in the annular space between the two mem- Is secured to the exbers.

The bell-like member I28 the power shaft I! by means of a theextreme'end-oi the member 128 between itself and a washer "2 which bears against the forward end of the cone III which, in

member I.

threaded into the tubular one to clamp in place an apertured plug member I which supports the A nut I38 screw the space I48, connected with the valve H2 and separates the high pressure channel from the drainage channel between the drain tube 36 and the breather tube 84.

The nuts I38 and I36 are secured against rotation relative to the power shaft upon which they are screw threaded by suitable locking pins I50 and the valve housing is restrained against rotation relative to the hub member 60 by similar locking pins I52.

The nut I38 has an extension received within an annulus in the flared portion of the bell member I28, and a leak proof seal I54 is provided between the end of the extension and the annulus. This construction provides between the members I44 and I38 a channel I56 for leading high pressure fluid, without leakage to the space I48 within the member I28.

When the hydraulic fluid in the channel I56 and the space I48 is at working pressure, this pressure through acting upon the end of the valve plunger I58 facing the space I48 fails to move the plunger against the action of the spring I62. The spring I62 has a carefully calibrated spring rate so that the plunger I58 takes a definite position in the casing I60 for each of the three operating pressures imposed on the hydraulic fluid, the pressures being hereinbefore referred to as the working pressure, the feathering pressure and, the restoring pressure.

An oil channel or conduit I64 (see Fig. 3) leads from the space I48 to the interior of the valve casing I60 and, when the valve is in the position incident to the working pressure of the hydraulic fluid, this channel is connected, through the reduced portion I66 of the valve stem, with a conduit I68 connected with the interior of the valve casing I60, leading around the tubular inner portion I24 of the valve housing, shown diagrammatically in Figs. 3 to 5 as extending through tube I24 for clearness of understanding, to the interior of the casing I of the by-pass valve generally indicated at II6. With the positions of the parts as illustrated in Figs. 1 and 2, the hydraulic fluid flows from the conduit I68 through the space between the ball I12 and the annular valve seat I14 formed in the casing I10, and through the conduit I16 to the channel I18, and out of the valve casing through the aperture I80 to the space at the rear of the piston.

If the ball valve I12 is unseated at the time that the flow from the passage I16 to the passage I68 begins, the action of the fluid against the face of the ball adjacent to the seat will maintain the ball in a position away from the seat. If the ball is seated at the beginning of the flow, or becomes seated during the flow, the pressure in the passage I16 will back up in the connected channel I18 and open the valve I82 permitting the fluid to flow from the valve seat I84 to the drain I85-35. The movement of the valve I82 will also bring the end of the memher 208 in contact with the ball I12 to unseat- 38 and the interior of the Cir through the conduit I68, past the ball and again establish the passage I18 to the passage I68. As far as the operation of the device is concerned, it is not material whether the fluid from the back of the piston drains from the valve The hydraulic fluid acting against the rear end of the piston I06 tends to urge the piston forwardly to increase the pitch of the propeller blades. If at any time the pitch of the propeller blades is too high, the valve operated by the governor I8, or a manual control, cuts off the high pressure fluid from the pump 24 and connects the high pressure fluid channel within the power shaft I2 with the sump 40, through the drain 39. When this occurs, hydraulic fluid under pressure in the space behind the piston drains through the conduit I16 past the ball I12,

the reduced portion I66 of the valve plunger I58, and through the conduit I64, back to the space I48 and out through the pressure fluid channel in the power shaft, Some of this hydraulic fluid under pressure may also move the hollow plunger I82 of the by-pass valve II6 forwardly to open a space between the rear end of the plunger and the cooperating valve seat I84 provided at the forward end of the channel I18 so that the hydraulic fluid may flow into the space between the outer and inner concentric members I26 and I24 to the forward end of the member I24, particularly illustrated in Fig. 3, where it enters the drain channel between the tubular member 34 and the tubular members I24 and 36. The oil released by the valve I82 flows into the space between the members I24 and I26 not occupied by the valve u casings I60 and I10. From this space the oil flows over the forward end of the member I24 to the interior of the tubular member I24 if a breather tube is not used, or to the space between the interior of the member I24 and the exterior of the breather tube 34 where such a breather tube is used. It will be noted that oil flow spaces are clearly indicated between the forward end of the member I24 and the adjacent surface of the breather tube in Fig. 2. When the space behind the piston is connected with drain, as indicated above, the propeller blades are turned toward their low pitch position by the action of centrifugal forces present in the blades themselves as they are rotated about the power shaft and the piston is forced rearwardly by the action of the cams 86 and 60 and the cam followers I02.

When hydraulic fluid under working pressure is applied to the rear of the piston I 06 for a sufficient interval, the piston will be moved forwardly until the ball I86 of the intermediate pitch stop mechanism, generally indicated at II4, rides up on the piston carried cam I88 which is moved under the ball by the longitudinal movement of the piston and the rotational movement of the piston due to the angularity of the cam slots 90. When this occurs (see Fig. 4), the ball I86 is forced upwardly between the balls I90 and I92 thereby imposing the force of the spring I64, through the movable abutment I86, the balls I92, I86 and I90 and the spacer I98 against the ball I12 to force the same into valve closing contact with the seat I14 to prevent the flow of hydraulic fluid past the ball I12 from the conduit I68 to the conduit I16. At the same time the hydraulic fluid under pressure forces the plunger I82 of the valve member II6 into sealing en-" gagement with the seat I84 at the end of the channel I 18 and, as the working pressure of the flow from the I12 or the valve I82.

assume hydraulic fluid not sufficient to compress the spring 288, which acts through the apertured abutment 282 against the ball 284, and move the ball 2B4 away from its seat 208 provided in the adjacent end of the tubular member tilt-"i secured in the end of the hollow plunger I82, the flow of hydraulic fluid under working pressure to the space behind the piston will be stopped at the end or the conduit I88, and there will be no iurther admission or hydraulic fluid to the space at the rear 01 the piston to move the propeller blades beyond the limiting high. pitch position determined by the relation of the cam I88 and the ball 188. Thus, when the hydraulic fluid is at the working pressure, the range of pitch changing movements or the propeller blades is limited by the low pitch limit stop M2 and the intermediate pitch limit stop II4. The cams I88 are formed on the interior surface of a sleeve member I88 having a splined connection ISI with the piston. This sleeve may inserted in the piston at any selected relative rotational position to determine the pitch angle at which the inter mediate pitch limit step will function and is sc-= cured in the piston by means such as the nut I 93.

When hydraulic fluid under feathering high pressure, which may be supplied by the pump 42, is applied to the space behind the piston, the piston is first moved forwardly in the manner described above for the working pressure, until the ball I88 oi the intermediate pitch liuiit stop device rides up on the cam I88 in the manner described above. While only one cam I88 is operative at a time, since the barrel may be mounted in any one of three different rotational positions, three cams have been provided so that one cam will be in a position to operate the pitch limiting valve regardless oi the rotational position of the barrel with respect to the propeller hub the cams being adjustable to provide any desired pitch angle for the intermediate stop. At the same time the valve plunger I58 is moved slightly forward but not suinciently to close the connection of the conduit I64 with the conduit I68 past the reduced portion I56 of the valve plunger so that hydraulic fluid under feathering high pressure flows through the conduit I64, the casing I88, the conduit I68 to the interior of the casing I18 of the valve II8. Although the ball I12 closes the passage to the conduit I18 when the ball I88 is on the cam I88, the pressure of the hydraulic fluid at feathering high pressure is suflicient to compress the spring 288 and open the valve passage between the ball 284 and the rear end of the member 208 as shown in Fig. 4. The hydraulic fluid then flows through the member 208, the apertured abutment 202, the hollow plunger I82 and the passage I18 to the space at the rear of the piston to continue the forward movement of the piston past the intermediate limit stop device. At the same time any hydraulic fluid that may have been trapped in the space between the front end or the piston and the interior of the forward portion of the cover member 94 may flow from that space through the conduit ZIII, the elbow M2 and the slot 2M into the interior of the for-yard portion 01 the valve casing I80, from which it escapes throughthe drain slot M8 to the interior or the outer wall I28 of the valve housing, and from this space around the forward end of the inner tubular member I24 of the valve housing and to drain through the v Hydraulic fluid at the feathering high pressure may be injected into the space behind the piston until the piston has been moved to its furtherest forward position as determined by :the limit stop 228 which is secured indirectly to the hub 14 and coacts with a lug in the movable cam member 84, and the propeller blades have been. rotated to a position in which they present only their edges to the relative wind.

Hydraulic fluid, such as engine lubricating oil, injected at th working or the feathering pressure into the space at the rear of the piston backs upin the interior of the barrel member 14 and fills the same thereby lubricating all the working parts or the propeller.- The packing means 18 and 80 between the barrel and the hub member and between the barrel and the base ends of the propeller blades, and sealing means between the two partsroi the barrel, render the barrel leak pr'ooi for hydraulic fluid at pressures up to and including the ieathering high pressure. Hydraulic fluid at pressures above the feathering high pressure is not permitted to flow into the barrel member.

When it is desired to restore the propeller irom a feathered condition to an operative condition, the auxiliary pump 42 is operated to apply the restoring high pressure to the hydraulic fluid supplied to the propeller operating mechanism.

when hydraulic fluid at the restoring pressure is supplied to the space I48, the valve plunger I58 is immediately moved forward to the position illustrated in Fig. 5 in which the valve piston 2Il on the valve plunger I58 interrupts the connectIon between the conduit I84 and the conduit I88 and the second valve piston 220 closes ofl the drain slot 2I8.

with the valve in the position indicated, the hydraulic fluid at restoring high pressure flows from the space I48 through the conduit I84, past the reduced portion I88 of the valve plunger, and

' then through the slot 2, the elbow M2 and the conduit 2I8 into the space between the forward end of the pis on I88 and the forward end of the cylindrical domed cover member 54, surrounding the forward end of the valve housing I20 and the extension member 222 which connects the forward end or the valve casing with the end of the cover member 88 and which is connected to the forward end or the outer wall I28 oi the valve housing by the integral transverse flange 224, which constitutes the front end wall of the valve housing. The hydraulic fluid under pressure is then, effective to act upon the forward end of the piston and force the piston rearwardly to restore the propeller blades to an operating condition.

While the piston is being forced rearwardly any hydraulic fluid which may have been trapped in the space at the rear of the piston flows through the conduit I16, past the ball valve I12 and through the conduit I88 into the valve casing I in a space occupied by a reduced portion 225 of the valve between the enlarged portion M8 and a piston member 228 and out of the valve casing through the apertures 23!! and 232 to the interior of the valve housing I28 from whence it flows to drain through the space between the tubes 34 and 38. It, for any reason, the ball I12 seats against the shoulder I14, as

when the piston is moving back past the intermediate pitch limit stop device II4, the drainage hydraulic fluid may alternatively flow through the channel I18, past the rear end or the valve plunger l82 into the interior of the va ve housmight become sufllcient to endanger the parts.

For this reason the .reliei valve generally indicated at 233 is provided between the space at the iorward end of the piston and the interior of the valve housing. This valve, as particularly illustrated in Fig. 3, comprises a tubular casing 234 which contains a compression spring 236 acting against an abutment 2'36which acts to force the ball 240 against the seat 242. The spring 236 is selected to maintain the relic! valve closed until a predetermined pressure or the hydraulic fluid in the'space at the trout of the piston is reached fluid seal connections 240' and 250 with the external surface of the outer shell I26 oi the valve housing, which are eflective to prevent the leakage of oil in either direction past the piston from the pressure side to the drain side.

While there has been illustrated and described a suitable mechanical embodiment oi what is now considered to be the preferred form oi the idea of the invention, it is to be understood that the invention is not limited to the construction so illustrated and described, but that such changes in the size, shape and arrangement of parts may be resorted to as come'within the scope of the subafter the valve will open to permit hydraulic I fluid to drain mm this space into the interior or the valve housing I20 and from thence to drain. when the piston I06 has been moved rearwardly a distance such that the intermediate pitch limit stop II4 has passed the cam I08, the limit stop device is restored to its operative condition and as soon as the restoring high pressure is removed from the hydraulic fluid, the propeller will again function as a constant speed or controllable pitch propeller within the range or pitch angle adjustment as determined by the limit steps 4 and I22 In the form of the invention illustrated the tube 34 extendsentirely through the propeller and the propeller operating mechanism and is connected with an annular vent between the nose plate 244, secured in spaced relation to the From the above description it will be observed that there has been provided a propeller that has two ranges or propeller blade pitch adjustment, that in one range the adjustment is accomplished by hydraulic fluid under pressure in one direction and by centrifugal action in the opposite direction. and in the second range of adjustment the adjustment is accomplished by hydraulic fluid under pressure in both directions, acting upon the opposite sides of the pitch controlling piston.

The area oi the end of the valve stem I58 facing the space I48 and the strength of the spring I62 are so related that the valve stem I56 does not change its position upon the imposition of hydraulic fluid under working pressure or materially change its position upon the imposition of hydraulic fluid at ieathering pressure into the space I40, but materially changes its position upon the imposition of hydraulic fluid under restoring pressure into the space I48. The piston portion 228 cooperates with the adjacent portion or the valve casing I60 to constitute a dash-pot "to regulate the movements of the valve stem I50 and prevent sudden movement or chattering oi the valve stem in the valve casing.

The piston I06 has a fluid seal connection 246 with the interior of the cover member 64 and propeller ior controlling the pitch changing joined claims.

Having now described the invention so that others skilled in the art may clearly understand the same what is desired by Letters Patent is as follows:

What is claimed is:

1. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, a fluid pressure 8C7 tuated power device for controlling the pitch changing movements of said blades, a positive low pitch limit stop and a positive high pitch limit stop for determining the entire range of pitch changing movement, and an intermediate pitch fluid controlling limit stop actuated by said power device to cut oil the fluid pressuresupply to said power device for normally limiting said pitch changing movements to the range of movement between one .01 said positive pitch limit stops and said intermediate pitch limit stop.

2. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movement, an expansible chamber fluid actuated mechanism carried by said movements of said blades, a positive high pitch limit stop and a positive low pitch limit stop for determining the entirerange oi pitch changing movements of said blades, an intermediate pitch fluid controlling limit stop operatively associated with'said mechanism and eflective within a selected range of pressure of the hydraulic fluid supplied to said mechanism to limit the pitch changing movement to the range between one of said positive pitch limit stops and said intermediate pitch limit stop, and means operative at a pressure of said hydraulic fluid higher than said selected pressure to render said intermediate pitch limit stop lneflectlve to limit the pitch changing movements of said blades.

3. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, an expansible' chamber hydraulic mechanism operatively connected with said blades for controlling the pitch changing movements thereof, a high pitch limit stop and a low pitch limit stop for determining the entire range of pitch changing movements of said blades, an intermediate hydraulic fluid controlling pitch limit stop operative under a selected pressure of the hydraulic fluid supplied to said mechanism to restrain said mechanism against moving said blades beyond a range determined by the operation of said intermediate pitch limit stop, means operative at a second selected pressure of said hydraulic fluid to render said mechanism operative to turn said blades to a pitch position beyond the limiting pitch position determined by the operation of said intermediate pitch limit stop, and means operative at a third selected pressure .01 said hydraulic fluid to render said mechanism operative to restore said blades 'to the range of pitch changing movement as detcrmined by said intermediate pitch limit stop.

4. In a controllable pitch propeller having blades rotatably mounted for pitch changing movement, an expansible chamber hydraulic mechanism having a relatively fixed part and a relatively movable part operatively connected with said blades and effective upon the application of hydraulic fluid under a selected pressure to one side thereof to turn said blades in one direction, an element movable by said movable part, a low pitch limit stop and a high pitch limit stop for determining the entire range of pitch changing ated by said element ata position intermediate the limits of said entire range of pitch changing movement to cut on the supply of hydraulic fluid to said one side of said relatively movable part,

and a by-pass valve operative at a pressure of said hydraulic fluid higher than said selected pressure to supply hydraulic fluid to the same side of said relatively movable member.

5. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movement, an expansible chamber hydraulic mechanism having a relatively fixed part secured to said hub, and a relatively movable part operatively connected with said blades and eflective upon the application of hydraulic fluid under pressure to one side thereof to turn said blades in a pitch increasing direction against the opposing force of the centrifugal action of the blades, an element movable by said relatively movable part, a low pitch limit stop and a high pitch limit stop for determining the entire range of pitch changing movement of said blades, a valve operated by said element at a position intermediate the limits of said entire range of pitch changing movement to cut of! the supply of hydraulic fluid at a selected pressure to said side of said relatively movable part, a bypass valve operative at a second selected pressure of said hydraulic fluid to continue the supply of hydraulic fluid to the same side of said relatively movable part through a range of pitch changing movement up to said high pitch limit stop, and a pressure responsive valve operative at a pressure of said hydraulic fluid higher than said second selected pressure to supply hydraulic fluid to the opposite side of said relatively movable part, and connect the space at the first mentioned side of said part with a drain.

movement of said blades, z valve oper- 1 movement up to said high pitch limit stop, and a pressure responsive valve operative at a pressure of said hydraulic fluid higher than said second selected pressure to supply ydraulic fluid to the opposite side of said relatively movable part, and connect the space at the first mentioned side of said part with a drain and a pressure relief valve between said opposite side of said relatively movable member and said drain.

7. In a controllable pitch=propeller having a hub and blades rotatably mounted in said hub for pitch changing movement, an expansible chamber hydraulic mechanism having a relatively fixed part secured to said hub, and a relatively movable part operatively connected with said blades and efiective upon the application of hydraulic fluid under pressure to one side thereof to turn said blades in apitch increasing direction against the opposing force of the centrifugal action of the blades, a valve operative at one se- 1 lected pressure to limit the application of hy- 6. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movement, an expansible chamber hydraulic mechanism having a relatively fixed part secured to said hub, and a relatively movable part operatively connected with said blades and effective upon the application of hydraulic fluid under pressure to one side thereof to turn said blades in a pitch increasing direction against the opposing force of the centrifugal action of the blades, an element movable by said relativelymovable part, a low pitch limit stop and a high pitch limit stop for determining the entire range of pitch changing movement of said blades, a valve operated by said element at a position intermediate the limits of said entire range of pitch changing movement to cut on the supply oi hydraulic fluid at a selected pressure to said side of said relatively movable part, a bypass valve operative at a second selected pressure of said hydraulic fluid to continue the supply of hydraulic fluid to the same side of said relatively movable part through a range of pitch changing third selected pressure ,to

,of said relatively movable said movable member to an intermediate pitch range, a valve operative at a second selected pressure to continue the application of hydraulic fluid to said movable member for the entire pitch range, and a valve operative at a third selected pressure to change the point of application of hydraulic fluid to said relatively movable member.

8. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movement, an expansible chamber hydraulic mechanism having a relatively fixed part secured 'to said hub, and a relatively movable part operatively connected with said blades and effective upon the application of hydraulic fluid under pressure to one side thereof to turn said bldaes in a pitch increasing direction against the opposing force of the centrifugal action oi the blades, a valve operative at one selected pressure to limit the application of' hydraulic fluid to said movable member to an inte mediate pitch range, a valve operative at a second selected pressure to of hydraulic fluid to said entire pitch range, and

movable member for the a valve operative at a reverse the application relative movable memvalve between the side member to which said third mentioned valve applies hydraulic fluid and a fluid drain.

9. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, an expansible chamof hydraulic fluid to said her and a pressure relief ber hydraulic mechanism having a relatively fixed part secured to said hub and a relatively movable part operatively connected with said blades and efl'ective upon the application of hydraulic fluid at pressures below a predetermined pressure to one side thereof toturn said blades in a pitch increasing direction against the opposing force of the centrifugal action of the blades, means for applying hydraulic fluid at said pressures below said predetermined pressure to said one side of said relatively movable member, means for con tinuously draining hydraulic fluid from the space at the opposite side of said relatively movable member while the pressure of said hydraulic fluid is below said predetermined pressure, means for supplying fluid at pressures above said predetermined pressure, and means operated by fluid at pressures above said predetermined pressure to reverse the relation of said hydraulic fluid applycontinue the application member, means connecting the space &

ing means and said drain means with respect to the sides of said relatively movable member.

10. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, an expansible chamber hydraulic mechanism having a relatively fixed part secured to said hub and a relatively movable part operatively connected with said blades and eflective upon the application of hydraulic fluid under a selected pressure to one side thereof to turn said blades increasing direction against the opposing force of action oi the blades and effective upon the application of hydraulic fluid under opposite side thereof to turn said blades in a pitch decreasing direction, means for applying hydraulic fluid under said selected pressure to the blade pitch increasing side of said relatively movable at the opposite side of said relatively movable member with a drain, and a pressure responsive valve operative at a selected pressure above said first mentioned selected-pressure to change the application oi hydraulic fluid under pressure to the blade pitch decreasing side of said relatively movable member and to connect the space at the opposite side of said relatively movable member with a drain.

11. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, an expansible chamber hydraulic mechanism having a relatively fixed part secured to said hub, and a relatively movable part operatively and effective upon the application of hydraulic fluid under pressure to one side thereof to turn said blades in a pitch increasing direction against the opposing force of the centrifugal action of the blades and effective upon the application of hydraulic fluid under pressure to the opposite side thereof to turn said blades in a pitch decreasing direction, a valve comprising an intermediate pitch limit stop for limiting the operative range of pitch increasing movements of said relatively movable member, a pressure responsive valve operative when said relatively movable member is in said operative range of pitch changing movements to vent the blade pitch decreasing side of said member and connect said pitch increasing side with said fluid under pressure and operative under a selected pressure of the hydraulic fluid to apply hydraulic fluid under pressure to the blade pitch decreasing side of said relatively movable member and connect the space at the blade pitch increasing side of said relatively movable member with drain through said intermediate pitch limit stop valve, and a by-pass valve for connecting the space at the pitch increasing side of said relatively movable member with drain arranged in parallel with said intermediate pitch limit stop valve.

12. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, an expansible chamber hydraulic mechanism having a relatively fixed part secured to said hub and a relatively movable part operatively connected with said blades and eiiective upon the application of hydraulic fluid under pressure to one side thereof to turn said blades in apitch increasing direction against the opposing force of the centrifugal action of the blades and efiective'upon the application of hydraulic fluid to the opposite side thereof to turn said blades in a pitch decreasing direction, means responsive to selected pressures of the hydraulic fluid supplied to said mechanism to render said mechanism operative to maintain the pitch pressure to the i the centrifugal assume changing movements of said blades within an operating range, to turn said blades to a feathered position and to restore said blades from said feathered position to said operative range, a single channel for the flow of hydraulic fluid in both directions when said mechanism is in said operative range and for the flow oi hydraulic fluid under pressure to said mechanism when said blades are being moved to or from their feathered position, and a separate channel for draining hydraulic fluid from said mechanism when said mechanism is operating outside of said normal operating range.

13. In a controllable hub and blades rotatably mounted in said hub for pitch changing movements, an expansible chamber hydraulic mechanism having a relatively fixed part secured to said hub and a relatively movable part operatively connected with said blades and effective upon the application oi? hydraulic fluid under one selected pressure to one side thereof to turn said blades in a pitch increasing direction, through an operative range of pitch changing movements and upon the application to the same side thereof of hydraulic fluid at a second selected pressure to turn said blades to a feathered position, and operative upon the application of hydraulic fluid at a third selected pressure to the opposite side thereof to restore said blades from the feathered position to said operative range, a vave constituting an intermediate pitch stop for restraining said relatively movable part against exceeding said operative range under said one selected pressure, a by-pass valve for rendering said relatively movable part operative to exceed said operative range under said second selected pressure, and a pressure responsive valve for rendering said relatively movable member operative to restore said blades from the feathered position to said operative range under said third selected pressure, said pressure responsive valve, and said intermediate pitch limit stop valve being arranged in series in the fluid line leading to said hydraulic mechanism, and said intermediate pitch limit stop valve and said by-pass valve being arranged in parallel.

i l. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, a cylinder secured to said hub, a piston in said cylinder operatively associated with said blades and.operative upon the application of hydraulic fluid at one selected pressure to one end thereof to turn said blades through an operative range of pitch adjustment in a pitch increasing direction against the opposing force of the centrifugal action of the blades, and operative upon the application to the same end thereof of hydraulic fluid under a second selected pressure to turn said blades to a feathered position, and an intermediate pitch stop device for restraining said piston against exceeding said operating range of pitch changing movement under said one selected pressure, said device comprising, a tubular casing having a valve seat therein, a ball in said casing cooperating with said valve seat, a spring, a movable ball for applying the force of said spring to said first mentioned ball, and a cam on said piston for moving said movable ball 15. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, a cylinder secured to said hub, a piston in said cylinder operatlvely associated with said blades and efiective upon the application of hydraulic fluid under one selected pitch propeller having a aasoms pressure to one end thereof to turn said blades in a pitch increasing direction through an-operative range of pitch adjustment, operative under a second selected pressure applied to the same end thereof to exceed said operative range and turn said blades to a feathered position, and operative under a third selected pressure applied to the opposite end thereof to restore said blades from the feathered position to said operative range, a fluid line and a drain line leading to said cylinder and a pressure responsive valve for reversing the application of hydraulic fluid under pressure from 7 one end of said piston to the other and for simultaneously reversing the connection of said drain line from the spaces opposite the respective ends of said piston, said valve comprising a tubular casing provided with spaced ports therein, a valve hydraulic fluid at a third selected-pressure to the opposite end thereof to restore said blades from the feathered position to said operativev range, and pressure responsive means eflective to change the application of hydraulic fluid from the blade pitch increasing side to the blade pitch decreasing side of saidpiston llDOnthl application thereto oi hydraulic fluid at said third selected pressure and to simultaneously provide a drain from the space at the blade pitch increased end of said piston..

plunger having. a plurality of valvepistons coopcrating with said ports and a pistonat one end subject to the pressure of said hydraulic fluid, and

saidgflades on said hub member, an expansible chamber hydraulic mechanism having a relatively flxed part secured to said barrel member a spring opposing movements of said plunger under the influence of the pressure of said bydraulic fluid, said spring having a rate such that "no material movement is imparted to said plunger by said flrst and second selected pressures but a material movement is imparted to said plunger b said third selected pressure. a,

16. In a controllable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, a cylinder secured to said hub, a piston in said cylinder operatively associated with said blades and effective upon the application of hydraulic fluid at one selected pressure to one side'thereof to turn said blades in a a '18-. In a controllable pitch propeller having a hub member adapted to be secured upon the end of a propeller shaft and provided with arms for rotatably receiving the propeller blades and a barrel member-surrounding said hub member and the adjacent ends of said blades to secure and a relatively movable part operatively connected with'said blades and effective upon the application thereto of hydraulic fluid at at least three graduated pressures to control the pitch of said blades in an operative range when subject to the lowest of said pressures, to turn said blades to a, feathered position when subject to the intermediate pressure and to restore said blades from said feathered position to said operative range'when subjected to the highest of c said pressures, means for directing the application of hydraulic fluid at said low and intermediate pressures to a space in said hydraulic mechanism connected with, the interior of said hub barrel and for directing the hydraulic fluid at'the highest pressure to a space in said hydraulic mechanism separated from the interior "of said barrel member by a hydraulic seal,

sures is permitted to enter .whereby hydraulic fluid at only the lower preshub barrel.

19. In combination with a hydro-controllable propeller having blades rotatably mounted for ppitch changing movements and a hydraulic casing. a hollow plunger, slidable in said casing cooperating at one' end with said valve seat, a valve seat in said plunger, a ball in said plunger and a spring in said plunger for urging said ball into closing relation with said valve seat, said spring having a rate such that hydraulic fluid under said one selected pressure will not move said ball away from said valve seat but hydraulic fluid under said second selected pressure will unseat said ball and flow into the space adjacent to mechanism for rotating said blades, and speed responsive means for controlling the pitch changing movements of said blades'within a predetermined range of pitch adjustment,

means for supplying hydraulic fluid at at least two different pressures to mechanism, a fluid passage in said propeller leading to said mechanisim'and valve means responsive to movements of said pitch changing mechanism to close said fluid passage at a particular position of themovable elementof said mechanism corresponding to a predetermined the end of said pisto said plunger cooperating with the valve seat in said casing to prevent the flow of hydraulic fluid into said space except past said plunger included valve. 1'7. In acontrollable pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movements, a cylinder secured to said hub, a piston in said cylinder operatively associated with said blades and effective upon the application of hydraulic fluid at one selected pressure to one end thereof to move said blades in a pitch increasing direction through a normal operative range against the opposing force of the centrifugal action of the blades, effective upon the application of hydrauhe fluid at a second selected pressure to the same end thereof to turn said blades past said normal operating range to a feathered posipitch angle and responsive toan increase in the pressure of the hydraulic fluid to reopen said flu d passage,

20. In combination with a hvdro-controllable propeller having blades rotatably mounted for pitch changing movements and a hydraulic mechanism for rotating said blades, and speed responsive means for controlling the pitch changing movements of said blades within a predetermined range of pitch adjustment, I

means for supplying hydraulic fluid at at least two different pressures to said hydraulic mechanism, a valve actuated by said'hydraulic mechanism to limit the pitch changing movements of said blades to said predetermined range, and a valve responsive to the higher of said pressures to bypass said mechanism actuated valve.

21. In combination with a hydro-controllable tion, and eflective upon the application of the interior of said said hydraulic comprising, a valve for directing the hydraulic fluid through said speed responsive device when subjected to the lower of said two pressures and for bypassing said speed responsive device when subjected to the higher of said two pressures, a valve responsive to movements of said hydraulic mechanism to cut of! the supply of hydraulic fluid from said responsive mechanism to said blade rotating mechanism when the mechanism reaches a predetermined point in its pitch changing movements, and a valve for opening a bypass around said out off valve when subjected to the higher of said pressures.

22. In combination, a controllable-pitch pro peller having a hub and blades-rotatably carried by said hub for pitch changing movements, an expansible chamber mechanism for controlling the pitch changing movements of said blades, means for supplying fluid under pressure to said mechanism, means for regulating the pressure or said fluid to at least two different values, a pair of opposed limit stops for determining the entire range of pitch changing movements of said blades, and an intermediate pitch limit stop actuated by said mechanism op erative at a predetermined pitch setting to cut oi! the supply of pitch changing fluid at one of said pressures to said mechanism but ineffective to cut off said fluid if the fluid pressure is increased to the other of said values.

23; In combination with a controllable-pitch propeller having a pitch changing mechanism operative to vary the propeller pitch through more than one range of pitch angles, means for supplying hydraulic fluid to said pitch changing mechanism at pressures within either of two different predetermined pressure ranges, a valve actuated by said pitch changing mechanism for restraining said mechanism against increasing the pitch of said propeller beyond a predetermined pitch angle when supplied with fluid at a pressure within the lower of said predetermin d ran es. a pressure responsive valve for rendering said first mentioned valve ineffective to restrict the action of said mechanism when said mechanism is supplied with fluid at a pressure within the higher of said predetermined ranges, and manually controllable means for selecting the pressure range of the fluid supplied to said pitch changing mechanism.

24. In a controllable-pitch propeller having a hub and blades rotatably mounted in said hub for pitch changing movement, a fluid pressure actuated motor carried by said hub and having a movable portion operatively connected with said blades to change thepitch thereof, a conduit for conducting hydraulic fluid at pressures within different selectable pressure ranges to said motor, a positive high pitch limit stop and a positive low pitch limit stop carried by said hub for determining the entire range of pitch changing movement of said blades, valve means operatively associated with said conduit in uding a movable element movable to a valve opening position by pressure of said fluid acting thereon and eifective upon movement thereof from a valve opening position to a valve closing position to interrupt the flow of fluid at pressures below a predetermined value to said motor and thus discontinue the operation of said motor by fluid from said conduit at pressures below said predetermined pressure, and means movable with the movable element of said motor operatively associated with the movable element of saidvalve means to close said valve and thus interrupt the flow of fluid from said conduit to said motor at a predetermined pitch angle between the pitch angles determined by said positive pitch limit stops.

25. In a controllable-pitch propeller having a hub and blades rotatably mounted in said hub for pitch changi g movement, a hydraulic motor carried by said hub having a movable part operatively connected with said blades to change the pitch-thereof, a positive low pitch limit stop and a positive high pitch limit stop carried by said hub for determining the entire range of pitch changing movement ,of said blades, and a conduit for conducting hydraulic fluid at pressures within difierent selectable pressure ranges to said motor to increase the pitch of the propeller blades and to vent exhaust fluid from said motor to permit the propeller blade pitch to decrease, valve means operatively associated with said conduit including an element movable to a valve opening position by the presure fluid position toblock said conduit and interrupt the flow of fluid to said motor and a check valve also operatively associated with said conduit to vent exhaust fluid from said motor when said conduit is blocked by said movable element, and a displacement element carried by the movable part of said motor and operatively engageable with the movable element of said valve to close said 'valve and thus interrupt the flow of fluid at. pressures within a predetermined low pressure range through said conduit to said motor at a predetermined pitch angle between the limiting pitch angles as determined by said positive limit stops.

26, In the combination of a hydraulically actuated controllable-pitch propeller and means for supplying pitch changing hydraulic fluid to said propeller at pressures within any selected one of different pressure ranges, a propeller hub, a plurality of blades rotatably supported in said hub for pitch changing movements, a hydraulic motor carried by said hub and having a movable member operatively connected with said blades for changing the propeller pitch, a single conduit extending between said fluid supplying means and saidmotor, and a valve carried by said hub and hydraulically connected with said conduit and with said motor at opposite sides of said movable element, said valve including an element movable by the pressure of the fluid in said conduit normally blocking the connection between said conduit and said motor at one side of said movable member while providing a connection between said conduit and said motor at the opposite side of said movable member, whereby said movable member will move in one direction upon the application of fluid under pressure to said motor through said conduit and said valve, said valve element being movable in one direction by an increase in the pressure of the fluid in said conduit above a in said conduit and movable to a,

predetermined pressure to connect said motor at said one side of said movable member with said conduit and block the connection between said conduit and said motor at said opposite side of said movable member and simultaneously open a fluid vent from said motor at said opposite side of said movable member, whereby said movable member will move in the opposite direction upon the application of hydraulic fluid at said increasedipressure through said conduit and said valve to said motor.'

27. In a controllable-pitch propeller having a hub, blades mounted in said hub for pitch changing movements, a double acting hydraulic mechanism operatively associated with said blades for changing the pitch thereof, means for supplying hydraulic fluid at diflerent selectable pressures, and a single conduit extending between said fluid supply means and said hydraulic mechanism for conducting fluid at said diflerent pressures, a valve having separate hydraulic connections, one with said single conduit and one with-each side of said double acting mechanism, said valve including an element subject to the fluid pressure in said conduit resiliently urged to a position opening a fluid passage from said conduit to a predetermined side of said hydraulic mechanism and movable by a predetermined increase in the pressure of the fluid in said conduit to close single conduit extending between said fluid.

supply means and said mechanism; a valve carried by said hub and disposed betweensaid mechanism and said conduiti said valve having a pair of ports connected one with each side of said double acting mechanism, a fluid passage 'one direction, said valve including a movable member having two operative positions effective to change the connection between said conduit, said vent and the respective ports upon moving from one of said operative positions to the other,

a spring resiliently urging said movable member to one of said operative positions, and a piston operatively connected with said movable member and having its face exposed to the fluid in said conduit to overcome the force of said spring and move said movable member to the other of said operative positions when the pressure of the fluid in said conduit exceeds a predetermined value, whereby the application of hydraulic fluid at pressures in excess of said predeter mined value through said conduit to said hydraulic mechanism willv change the pitch of said propeller in the opposite direction.

JOHN ELMER ANDERSON. MURRAY C. BEEBE. 

